One conventional practice is to impregnate one or more drops of fluid samples to be analyzed onto a solid sample carrier, dry the solid sample carrier impregnated with the fluid, and then send the solid sample carrier to a laboratory for analysis. The fluid to be analyzed can be, for example, blood of a newborn baby and the solid sample carrier can be, for example, a sheet of filter paper or some other suitable material which is able to carry the fluid to be analyzed. In the laboratory, one or more pieces containing the dried fluid to be analyzed are cut off from the solid sample carrier and the one or more pieces that have been cut off are conveyed, for further analysis, to one or more sample wells of e.g. a microtitration plate or some other sample well element. Each piece can be cut off from the solid sample carrier for example with a punch and a die provided with a channel for the punch, where the punch is arranged to cut off the piece with a single stroke through the solid sample carrier. It is also possible to use a cutting instrument capable of producing a localized, point-form cut on the solid sample carrier and to move the point-form cutting impact produced by the cutting instrument along the outer periphery of each piece so as to detach the piece from the solid sample carrier. Another conventional practice is to handle the sample to be analyzed in liquid form so that the sample is blended or dissolved in sample carrier liquid. In this case, one or more drops of the sample carrier liquid containing the sample are dispensed to one or more sample wells for further analysis.
The analysis of a sample contained by a sample well can be based on for example labeled analyte-specific tracer molecules where concentrations of one or more analytes in the sample can be detected on the basis of changes taking place in luminescence, e.g. fluorescence, emission signals measurable from the sample well. Analysis methods of the kind mentioned above are for example methods based on the fluorescence resonance energy transfer “FRET”. Details about exemplifying FRET-based analysis methods can be found for example from publications US20060147954 and V. Laitala et al., Time-resolved detection probe for homogeneous nucleic acid analyses in one-step format, Analytical Biochemistry 361 (2007) 126-131.
Prior to carrying out an analysis of the kind mentioned above, it is important to ensure that a sample is present in a sample well. The absence of the sample may cause an erroneous negative or positive result. A known method for detecting whether a sample well contains a sample is based on light absorbance caused by a piece of a solid sample carrier or substances dissolved from the piece to reagents in the sample well. An inherent limitation of the method based on the absorbance is the need to use a transparent microtitration plate or other sample well element. In many cases there is, however, a need to use or it may be advantageous to use a light impervious microtitration plate or other sample well element. In these cases, the above-mentioned method is not applicable or at least some advantages are lost. Another known method for detecting whether a sample well contains a sample is based on luminescence intensity which is dependent on the presence of the sample and/or a piece of a solid sample carrier and/or substances dissolved from the piece to reagents in the sample well. In conjunction with some analysis methods, the use of the method based on the luminescence intensity may be challenging because the effect of the sample and/or the sample carrier on the luminescence intensity may be case specific and/or non-deterministic.
In the context of this document the term “solid” means that material under consideration is in none of the following phases: gas, plasma, and liquid.
In the context of this document, the term “solid” does not exclude porousness and other kind of ability to be impregnated with liquid. Therefore, in the context of this document, solid material can be porous or otherwise capable of being impregnated with liquid. Furthermore, the term “solid” does not exclude plasticity, elasticity, and flexibility of material under consideration. Yet furthermore, the term “solid” does not exclude mosaic structure of an object under consideration.
In the context of this document, the term “solid sample carrier” means a carrier made of solid material, e.g. a sheet of filter paper, capable of carrying sample material and the term “sample carrier liquid” means liquid capable of carrying sample material.